This proposal will address the role of dopamine in psychotic disorders by means of 3 approaches: 1) In rats the uniqueness of prefrontal cortex as a target area for antipsychotic drugs (APD) will be assessed by acute and chronic administration of various APD and measurement of homovanillic acid (HVA) in caudate and prefrontal cortex; 2) in rats prefrontal cortex will also be examined as a possible unique site of action for drugs which can produce psychotic disorders; 3) in patients, plasma HVA and MHPG will be studied with respect to their status as markers for early neuroleptic response in acute psychosis. Promising pilot data has been obtained for each of these areas of study.